Bioluminescence

In the darkness of the deep ocean, where sunlight never reaches, the water is nonetheless dotted here and there with tiny points of living light. A remarkable number of creatures, from microscopic plankton to large fish, are able to produce their own light through a process called bioluminescence. Rather than generating heat in the way an ordinary lamp does, this light is created by a chemical reaction inside the organism's own body, which makes it extraordinarily （ 1 ）: almost all of the energy becomes light, and very little is wasted.

Animals use their light in surprisingly varied ways. Some deep-sea fish dangle a glowing lure in front of their mouths to draw curious prey within easy reach of their jaws. Others release a sudden bright flash to startle an attacker, or a cloud of glowing particles to confuse it while they make their escape. Many use light simply to find or signal a mate in the surrounding darkness. （ 2 ） the deep sea, bioluminescence also appears in fireflies on land and in certain fungi, which shows just how widely and how often this useful ability has evolved.

Scientists have found clever ways to put this natural glow to practical use. The same molecules that make these creatures shine can be attached to cells in the laboratory, allowing researchers to watch processes that would otherwise be completely invisible, such as the spread of a disease through the body or the moment when a particular gene becomes active. （ 3 ）, bioluminescence has become not only one of nature's most beautiful displays but also a genuinely valuable tool for understanding life itself.